Glaucoma

What is Glaucoma ?

 

Glaucoma is a group of diseases that can damage the eye's optic nerve and result in vision loss and blindness. Glaucoma occurs when the normal fluid pressure inside the eyes slowly rises. However, with early treatment, you can often protect your eyes against serious vision loss.

What is the optic nerve ?
The optic nerve is a bundle of more than 1 million nerve fibres. It connects the retina to the brain. The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision.

 

What are the forms of glaucoma?

Open-angle glaucoma is the most common form. Some people have other forms of the disease :

• Low-tension or normal-tension glaucoma.  Optic nerve damage and narrowed side vision occur in people with normal eye pressure. A comprehensive medical history is important in identifying other potential risk factors, such as low blood pressure, that contribute to low-tension glaucoma. If no risk factors are identified, the treatment options for low-tension glaucoma are the same as for open-angle glaucoma.
• Angle-closure glaucoma.  The fluid at the front of the eye cannot reach the angle and leave the eye. The angle gets blocked by part of the iris. People with this type of glaucoma have a sudden increase in eye pressure. Symptoms include severe pain and nausea, as well as redness of the eye and blurred vision. If you have these symptoms you need to seek treatment immediately. This is a medical emergency !
• Congenital glaucoma.  Children are born with a defect in the angle of the eye that slows the normal drainage of fluid. These children usually have obvious symptoms such as cloudy eyes, sensitivity to light and excessive tearing. Surgery is safe and effective. If surgery is done promptly, these children usually have an excellent chance of having good vision.
• Secondary glaucomas.  These can develop as complications of other medical conditions. These types of glaucomas are sometimes associated with eye surgery or advanced cataracts, eye injuries, certain eye tumors, or uveitis (eye inflammation). Pigmentary glaucoma occurs when pigment from the iris flakes off and blocks the meshwork, slowing fluid drainage. A severe form, called neovascular glaucoma, is linked to diabetes. Corticosteroid drugs used to treat eye inflammations and other diseases can trigger glaucoma in some people. Treatment includes medicines, laser surgery, or conventional surgery.

Causes and Risk Factors

How does open-angle glaucoma damage the optic nerve?
In the front of the eye is a space called the anterior chamber. A clear fluid flows continuously in and out of the chamber and nourishes nearby tissues. The fluid leaves the chamber at the open angle where the cornea and iris meet. (See diagram) When the fluid reaches the angle, it flows through a spongy meshwork, like a drain, and leaves the eye.
Sometimes when the fluid reaches the angle, it passes too slowly through the meshwork drain. As the fluid builds up, the pressure inside the eye rises to a level that may damage the optic nerve. When the optic nerve is damaged from increased pressure, open-angle glaucoma and vision loss may result. That is why controlling the pressure inside the eye is important.

Does increased eye pressure mean that I have glaucoma?

Not necessarily. Increased eye pressure means you are at risk of developing glaucoma, but does not mean you have the disease. A person has glaucoma only if the optic nerve is damaged. If you have increased eye pressure but no damage to the optic nerve, you do not have glaucoma. However, you are at risk. Follow the advice of your eye-care professional.

Can I develop glaucoma if I have increased eye pressure?

Not necessarily. Not every person with increased eye pressure will develop glaucoma. Some people can tolerate higher eye pressure better than others. Also, a certain level of eye pressure may be high for one person but normal for another.
Whether you develop glaucoma depends on the level of pressure your optic nerve can tolerate without being damaged. This level is different for each person. That is why a comprehensive dilated eye exam is very important. It can help your eye-care professional determine what level of eye pressure is normal for you.

Can I develop glaucoma without an increase in my eye pressure?

Yes. Glaucoma can develop without increased eye pressure. This form of glaucoma is called low-tension or normal-tension glaucoma. It is not as common as open-angle glaucoma.

What can I do to protect my vision?

Studies have shown that the early detection and treatment of glaucoma, before it causes major vision loss, is the best way to control the disease. So, if you fall into one of the high-risk groups for the disease, make sure to have your eyes examined through dilated pupils every two years by an eye-care professional.
If you are being treated for glaucoma, be sure to take your glaucoma medicine every day. See your eye-care professional regularly.

 

What are the symptoms of glaucoma?

At first, there are no symptoms. Vision stays normal and there is no pain.
However, as the disease progresses, a person with glaucoma may notice his or her side vision gradually failing. That is, objects in front may still be seen clearly, but objects to the side may be missed.
As glaucoma remains untreated, people will slowly lose their peripheral (side) vision. They seem to be looking through a tunnel. Over time, straight-ahead vision may decrease until no vision remains.
Glaucoma can develop in one or both eyes.

 

Success and post-operative complications

The success rate of a trabeculectomy is approximately 65-70%. Additional 20% can have a qualified success, meaning the goal IOP is achieved using one or more anti-glaucoma medication(s) postoperatively. Approximately 10-15% of a trabeculectomy may fail in the first few months due to excessive conjunctival scarring. In approximately 1% of the time however, there can be more serious complications such as haemorrhage (bleeding), infection and other complications. Depending on the complication, it may result in temporary or even permanent reduction in vision. It may also require further surgical procedure to correct the complication. It is important to discuss these potential complications with the treating physician before surgery.

The most common short-term complication of trabeculectomy surgery is that it may fail to adequately lower the IOP. This may occur due to the excessive scarring of the conjunctival tissue with decreased filtration of the aqueous fluid out of the eye. On the other hand, the IOP may be too low (called hypotony) due to the excessive filtering of the aqueous fluid or leaking wound. Low IOP (typically below 5 mmHg) can cause blurry vision and can be associated with shallowing of the anterior chamber, cataract formation and a greater risk of intraocular fluid accumulation (choroidal effusion) or intraocular bleeding (suprachoroidal haemorrhage). The suprachoroidal haemorrhage is a particularly feared complication after trabeculectomy because it is often associated with pain, elevated IOP and a permanent decrease in vision. It often requires additional surgery to drain the blood.

There are also long-term complications of having a trabeculectomy bleb around the eye. If there is a leak from the bleb, the IOP may become too low. In addition, the bleb leak can increase the risk of infection. An infection in a post-trabeculectomy eye can be serious because the surgical hole in the sclera may allow direct access of  the offending micro-organism to the inside of the eye. Such intraocular infection can seriously compromise the vision and even the integrity of the eye itself. Therefore any symptoms of infection in a post-trabeculectomy eye such as pain, decreased vision, redness and purulent discharge should be reported and examined promptly. This may occur even years after the surgery. For this reason, post-trabeculectomy patients are encouraged always to wear goggles during swimming and are discouraged from wearing contact lenses in order to decrease the possibility of a bleb infection (called blebitis or bleb-associated endophthalmitis).

Even successful trabeculectomy surgery may not last forever; the surgery is considered successful if it controls the IOP for a period of 7-8 years. If the first trabeculectomy fails, it can be repeated a second (rarely third) time to control glaucoma. Subsequent trabeculectomies usually have a higher chance of failure than the primary trabeculectomy surgery. If trabeculectomy fails to control glaucoma adequately, the surgeon may consider a glaucoma drainage tube (or seton).

All complications can be treated medically or surgically. Serious, vision-threatening complications are uncommon. If they occur, additional medication or surgery may be needed.